1. Field of the Invention
This invention relates to water-soluble polymers and, more particularly, to a method of rapidly dissolving such polymers in water.
2. Description of the Prior Art
The use of solutions of water-soluble polymers in thickening and flocculating applications is well known. Such applications include the clarification of aqueous solutions in papermaking, and in treatment of sewage and industrial wastes. Such solutions of polymers are also useful as stabilizers for drilling muds, and in the secondary recovery of petroleum by waterflooding.
Although these polymers are most often available commercially as powders or as finely divided solids, they are most frequently utilized in aqueous solutions. This necessitates that the solid polymer material be dissolved in water. Although the various polymers are more or less soluble in water, difficulty is often experienced in preparing aqueous polymer solutions because of their slow dissolution and because the solid polymer is not readily dispersible in water.
Furthermore, dispersion of solid polymers in water is hindered by their tendency to clump or remain as agglomerates on contact with water. Lumps of solid polymer immediately form by the encapsulation of undissolved solids in an outer coating of water-wet polymer which retards the penetration of additional water into the agglomerate. Although many of these lumps are eventually dissolved by continued agitation, it is frequently impractical to agitate the solution for a sufficiently long period to obtain complete dissolution.
The foregoing problems are described in U.S. Pat. Nos. Re. 28,474 (Jul. 8, 1974) and U.S. Pat. No. Re. 28,576 (Oct. 21, 1975) issued to Anderson et al., the respective disclosures of which are hereby incorporated by reference.
The above-identified Anderson et al reissue patents describe a method of rapidly dissolving water-soluble polymers in which a polymer is dispersed into a water-in-oil emulsion, which emulsion is then inverted in water to release the polymer into solution. The Anderson et al disclosures require an oil-to-water ratio between 5:1 and 1:10.
According to the Anderson et al disclosures, emulsions containing between 5 and 75 weight percent polymer dispersed therein can be prepared and inverted into aqueous solution. However, it has been found in practice that the upper limit of the polymer content of an emulsion made according to the Anderson et al process is much lower than 75 weight percent, and usually is in the 10-35 weight percent range, depending upon the characteristics of the particular emulsion.
Further, the Anderson et al system, in practice, requires substantial amounts (e.g. 20 wt. %, or more, based on oil) of an emulsifier in the oil/water/polymer emulsion to provide a stable product.